1. Field of the Invention
The present invention relates to a laser microscope having a spectrophotometric unit which obtains spectral data for light from a sample, especially for fluorescence.
2. Description of the Background Art
Conventionally, there is known a laser microscope which converges a laser beam onto a sample via an objective lens, incorporates light, e.g., fluorescence from the sample into a spectrophotometric unit via an optical fiber, and obtains spectral data for the fluorescence.
This type of laser microscope is disclosed in Jpn. Pat. Appln. KOKAI Publication Nos. 5-142144 and 2000-56244. Especially, Jpn. Pat. Appln. KOKAI Publication No. 2000-56244 discloses a laser scanning microscope. This laser scanning microscope includes a scanning apparatus which comprises a laser light source unit, a dichroic beam splitter, an XY optical scanner, a confocal pinhole, a light detector, etc. The laser scanning microscope includes a spectrophotometric unit such as a diffraction grating connected by an optical fiber. The laser light source unit oscillates light having a plurality of wavelengths. The dichroic beam splitter reflects light from the laser light source and transmits fluorescence from a sample. The laser scanning microscope irradiates a laser beam from the laser light source unit onto a sample via the scanning apparatus by performing two-dimensional scanning. The laser scanning microscope incorporates fluorescence from the sample via the dichroic beam splitter and the optical fiber of the scanning apparatus into the spectrophotometric unit. The laser scanning microscope accumulates spectral data for each scan pixel and finally acquires spectral data for all scan pixels on an image.
On the laser scanning microscope of this kind, however, the laser wavelength to be irradiated onto a sample depends on a fluorescent dye to be used. For this reason, there is provided a plurality of types of dichroic beam splitters according to types of fluorescence from a sample or laser wavelengths to be used. One of a plurality of splitters is appropriately selected so as to be positioned on an optical path according to observation conditions.
When a plurality of dichroic beam splitters is selectively used so as to be positioned on the optical path, however, fluorescence imaged at the end face of an optical fiber may be misaligned due to angle errors of respective dichroic beam splitters. When a dichroic beam splitter on the optical path is changed to another, for example, it is assumed that there occurs a change of 2′ ({fraction (1/30)} degrees) of respective dichroic beam splitters before and after the change. In this case, assuming that there is a focal length of 200 mm for a lens to form an image on the optical fiber end, there occurs a deviation of 200×tan (2′×2)=0.233 mm. If the optical fiber is assumed to have a core diameter of 100 μm, the fluorescence may not be completely incident on the end face of the optical fiber due to misalignment of the fluorescence center. In view of these facts, a loss of much incident fluorescence is caused and may hamper the spectral data acquisition.
In order to minimize a fluorescence loss, one possible solution is to enlarge the optical fiber's core diameter approximately up to 1 mm and allow the entire fluorescence to be incident on the end face of the optional fiber despite misalignment of the fluorescence center. However, the use of such optical fiber with a large diameter increases an area of light output toward the spectrophotometric unit. Thus, a light volume loss due to an incident slit inserted to the incident optical path for a spectroscope is increased and may hamper the spectral data acquisition.